The recent upgrading of cars has requested to enhance the quality of each automotive part. Noise reduction of the automotive parts has become one of the problems to be solved. There is also a demand for improvement of the grease performance to reduce the noise of automotive parts. As for the grease performance, there is another demand for the temperature properties covering a wider range (from high temperatures to low temperatures).
Addition of a polymer, which is a measure taken to reduce noise has achieved the goal to some extent. For example, there is disclosed a grease composition provided with noise reduction performance by adding a ultra-high molecular weight polyolefin powder (Japanese Patent Unexamined Publication (JP Kokai) Hei 07-173483).
However, the base oils and polymers with high viscosities are inferior in fluidity at low temperatures (due to their high pour points), so that the operating temperature region will be limited. Accordingly, both properties may not be satisfied according to the selection of base oils and polymers.
Further, the grease where the polymer powders are added as mentioned above has the drawback of short life because the grease may be hardened upon heating.